1. Field of the Invention
This invention relates to an ink jet head which performs recording by discharging ink utilizing the heat energy generated by an electrothermal transducer, a substrate to be used for formation of said head, and an ink jet apparatus equipped with said head.
2. Related Background Art
Ink jet system described in U.S. Pat. Nos. 4,723,129, 4,740,796, etc. (namely bubble jet system called by Canon K. K.) can perform recording of high precision and high quality at high speed and high density and, s also suitable for color formation, and compaction, which is attracting increasing attention in recent years. In a representative example of the device to be used for this system, there exists a heat acting portion which permits heat to act on ink for discharging ink (liquid for recording, etc.) by utilizing heat energy. That is, by providing a heat-generating resistor having a heat-acting portion corresponding to an ink pathway, ink is abruptly heated to form bubbles by utilizing the heat energy generated from the heat-generating resistor and ink is discharged through the bubble formation.
The heat-acting portion is apparently similar in part to the constitution of the so called thermal head of the prior art from the standpoint that heat is permitted to act on an objective material, but the fundamental technique is greatly different in the point that the heat-acting portion is directly in contact with ink, the point that the heat-acting portion is exposed to mechanical shock brought about by cavitation by repeated bubble formation and bubble extinction of ink, further erosion in some cases, and also the point that the heat-acting portion is exposed to elevation and dropping of temperature approximately by 1000.degree. C. within an extremely short time on the order of 10.sup.-1 to 10 micro-seconds. Therefore, the thermal head technique cannot be applied to the bubble jet technique as a matter of course. Thus, it is impossible to discuss the thermal head technique and the ink jet technique within the same category.
Whereas, as the material of the heat-generating resistor constituting the electrothermal transducer possessed by the ink jet recording head, because it becomes very high in temperature, materials which are stable even under high temperature state and also excellent in oxidation resistance have been employed, such as nitrides, carbides, silicides, borides of high melting metals, transistion metals, etc.
In recent years, in response to the demands of high density recording and high speed recording in ink jet apparatus by use of ink jet recording head, the method of increasing the power applied on a heat-generating resistor or shortening the pulse width of current width is going to be employed. In that case, the heat-generating resistor is heated to further higher temperature, and therefore a heat-generating resistor having higher heat resistance is demanded.
Also, when the size of the heat-generating resistor is made smaller for increasing the recording density, the area resistance of the heat-generating resistor is made substantially constant, and therefore only the resistance value as the electroconductor in the plural number of heat-generating resistors as a whole is increased, whereby the electric power consumption will be increased in the plural number of the heat-generating resistors as a whole.
Further, power increase leads to enlargement of IC capacity for driving, which increase of IC capacity in turn brings about elevation of the cost of ink jet head, etc.
Accordingly, in order to correspond to demands for high density recording, high speed recording, while reducing electric power consumption, for example, various methods for enhancing specific resistance of heat-generating resistors have been investigated.
For example, as the method for enhancing specific resistance without changing the shape or, the film thickness of a heat-generating resistor, there is the method of adding nitrogen, oxygen, etc. as the component at a predetermined ratio in the composition of the heat-generating resistor in order to obtain a desired specific resistance.
On the other hand, there has been also known the method of effecting higher resistance by changing the film thickness of heat-generating resistor without changing its material.
However, according to the investigations by the present inventors, in the heat-generating resistor made to have higher resistance by the method of adding nitrogen, oxygen, etc. as mentioned above, increase of electric power consumption accompanied with great reduction in resistance value was observed as the driving electric power was increased. This may be considered to be due to the fact that most of the components added exist in the state free from the heat-generating resistor forming compound which is the base.
On the other hand, when specific resistance is increased by making thinner the film thickness of the heat-generating resistor, since the film thickness is required to be controlled correctly in this region, a problem is involved in stability of production. Moreover, the effect of gas and, moisture absorption on the heat-generating resistor surface appears to worsen the stability of the heat-generating resistor itself, and therefore the advantage is further smaller as compared with the increase of resistance of the heat-generating resistor by addition of nitrogen, oxygen, etc. as described above.